Trachoma is the world's leading cause of preventable blindness. This disease, caused by Chlamydia trachomatis, is endemic in many parts of the developing world. Several years ago in a project called Azithromycin in Control of Trachoma (ACT I) we evaluated the use of community-wide treatment with oral Azithromycin. This approach resulted in clinical improvement and dramatic reduction in prevalence of chlamydial infection through a 1- year follow-up. We now propose to return to these villages and do clinical surveys to assess trachoma activity, and to test conjunctival swabs for the presence of C. trachomatis by ligase chain reaction (LCR). The villages will include the previous treatment sites (oral) azithromycin versus topical tetracycline) as well 2 new villages that have not had any prior treatments. Thus we will determine the longterm (5 year) effects of the azithromycin, and follow them for 3 years. We will compare single-dose treatment with the 3 doses used in ACT I to determine the efficacy of this simpler, less expensive regime. All LCR positive specimens from the ACT I villages will have the major outer membrane gene amplified and sequenced. The genovars will be mapped for location within villages and families and then their distribution will be followed over time, after treatment to provide a better understanding of the epidemiology of the infection. Results of the study will be used as data input for the generation of mathematical model to predict whether community-wide retreatment (or alternate strategies) will be needed, and the optimal timing for such retreatment. In sum, this study should provide a rational approach to use of community-wide azithromycin treatment to eliminate blinding trachoma as a public health problem.